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Poisonous animals
 
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Genus/Species

 

Tetrodotoxic fish: Puffers and their relatives

Species

  1. Tetraodontidae (genera Amblyrhynchotes, Arothron, Boesemanichys, Chelonodon, Ephippion, Fugu, Lagocephalus, Sphaeroides, Tetraodon, Torquigener)
  2. Diodontidae (genera Chylomycterus, Diodon)
  3. Canthigasteridae (genus Canthigaster)

Other members of Tetraodontiformes may also be potentially toxic.

Taxonomy

Pisces; Osteichthyes; Tetraodontiformes; Tetraodontoidei

Common names

  1. Puffers, Globefishes, Balloonfishes, Kugelfische, Fugu
  2. Porcupinefishes, Igelfische 
  3. Sharp-nosed puffers, Spitzkopfkugelfische

Distribution

  1. Tropical and warm seas in a circumglobal belt between the latitudes of approx. 47°N and 47°S. Some species (Tetraodon sp., Sphaeroides sp., among others) also in fresh water and brackish water
  2. Tropical and warm seas
  3. Tropical and subtropical seas

 

 


Fig. 4.8  Fugu rubripes rubripes

Biology

Poisoning caused by Puffers and their relatives has been known for a long time. The cause can be traced to tetrodotoxin, one of the most potent non-protein natural substances, which is found throughout the body in these fish. The highest concentrations of toxin are found in the skin, the ovaries and the liver.

The name Puffer refers to the ability of these already rotund fish to puff themselves up into a spherical shape by taking in water when in danger. When Porcupinefishes do this, the spines distributed on their upper body radiate outwards, thus offering additional protection against predators.

They inhabit coastal waters, typically coral reefs, but also tropical bodies of freshwater. The skin has no scales and their teeth are fused into a parrot-like beak with which they can efficiently "crack" hard-shelled prey such as crabs or shellfish, but also hard corals. The propeller-like use of their fins allows these slow-swimming fish to be extremely agile in a small space.

It is not clear to what extent other members of the Puffer family (Tetraodontiformes), such as Triggerfishes (Ballistidae), Trunkfishes (Ostraciontidae) or Molas (Molidae), contain tetrodotoxin. Tetrodotoxin has been detected in a number of much less closely related animals, both vertebrates and invertebrates. It has been found in Gobies (Gobius criniger and Yongeichthys criniger), marine snails (e.g. Babylonia japonica, Nassarius sp., among others), flatworms (Planocera multitentaculata), starfish (Astropecten sp.), crabs (e.g. Zozimus sp.) and in the Blue-ringed octopus (Hapalochlaena maculosa). Tetrodotoxin has also been detected in animals outside the marine environment, namely in the spawn of the California newt Taricha torosa and in the gland secretions of atelopid frogs of the Atelopus genus. These new findings suggest that tetrodotoxin cannot be a toxin that is synthesised by Puffers themselves. The probability that so many different types of animals could produce an identical toxin of such complexity is practically zero.

In the meantime several strains of bacteria have been discovered that can synthesise tetrodotoxin and that can find their way into Puffers via the food chain.

Risk

Puffer poisoning is often dangerous. It is common in Japan, where Puffers ("Fugu") are prepared in the traditional manner and eaten as a delicacy. Areas from which tetrodotoxin poisoning has been reported include Japan, Taiwan, China, Hong Kog, Thailand, Korea, Singapore, Malaysia, Australia, the United States, Kiribati, Papua New Guinea and Fiji. In other regions tetrodotoxin poisoning is only rarely a cause of fish poisoning.

Most cases of Pufferfish poisoning are caused by ingestion of toxic livers. Between 1886 and 1963, 10,745 cases were recorded in Japan, with a mortality rate of almost 60% (!) (Halstead 1967). More recent data from Japan indicate a much lower mortality rate of barely 7% in a total of 488 patients in the years 1987–1996 (Yoshikawa-Ebesu et al. 2001).

The preparation of Pufferfish in Japanese Fugu restaurants requires a licence and is generally only carried out by specially trained chefs. Different species of Puffers, in particular members of the Fugu genus, are prepared in these restaurants. The highly poisonous parts such as the skin and viscera are removed and the weakly toxic flesh is further detoxified through several processes. Poisoning practically never occurs after consumption of fish in a Fugu restaurant, but rather is usually the consequence of incorrect preparation of fish by laypersons.

Puffers and their relatives can also cause ciguatera poisoning.

Literature (biological)

Halstead 1967, 1988, 2001a, Auerbach and Halstead 1989, Mebs 1992, Yoshikawa-Ebesu et al. 2001